1. Field of the Invention
This invention relates generally to a combustor of a gas turbine engine and, more particularly, to a system and method of detecting partial flame out in a gas turbine engine combustor.
2. Description of Related Art
The combustor in a gas turbine engine is utilized to perform the function of burning a mixture of fuel and compressed air to produce gasses which drive one or more turbines located downstream thereof. It is well known that the amount of fuel burned by the combustor (i.e., the fuel-to-air ratio) has an effect on the production of such combustion gasses. Thus, as less fuel is burned, the temperature in the combustion chamber is lowered, less combustion gasses are produced, and the turbine output of the engine is decreased. When a combustor does not burn all of the fuel supplied to it, such as during a partial flame out, overall engine performance and efficiency suffers.
In the case of combustors designed specifically for low emissions, such as a triple annular combustor of the General Electric Company known by the designation LM6000 Dry Low Emissions (DLE), partial blow out of the flame therein has an even greater impact. As noted above, partial flame out is one cause for a drop in the temperature in the combustion chamber. Because the LM6000 DLE gas turbine engine is designed to maintain delivered power, the engine control will cause additional fuel to be added to the combustor. However, adding fuel to a combustor which does not burn it all has the adverse consequence of producing a high level of emissions and unburned hydrocarbons which is contrary to the goals of a low emissions combustor. Moreover, the excess fuel supplied to the combustor is wasted.
It should be noted that flame out of the entire combustor has a drastic effect which is easily recognized since the engine will be unable to continue operation. However, partial flame out of the combustor is more difficult to detect since the consequences thereof may only be slight with regard to the overall engine operation. This is because flame out may occur in only a few localized combustion regions. The causes of such localized or partial flame out are varied (e.g., combustor geometry, localized cooling/bleed flows, etc.), but the end result is that the fuel/air ratio is not conducive to being ignited. It has been found that partial flame out of the LM6000 DLE combustor typically occurs during the transition between combustor operating modes, such as when an annular combustor located radially inward or outward of the pilot dome is being activated. While the activation of these other domes is dependent upon the pilot dome for ignition, it can occur only in the combustion regions where the carburetor devices are able to provide the necessary fuel/air ratio.
Given the adverse effects of combustor flame out, various systems have been developed to detect this condition. One such system is a flame detection measurement system that utilizes sensors to detect the presence or absence of flame at predetermined locations. It has been found that this type of flame detection system is highly dependent upon the location and reliability of the sensor. Because such sensors are a mechanical device prone to wear, failure, and environmental conditions, they have not provided the high degree of reliability required. Moreover, the placement of sensors within the combustor has oftentimes made it difficult to detect localized flame out in the combustor. In addition, flame detection measurement systems are generally expensive to supply and maintain for production.
A second type of flame detection system is one which measures exhaust gas. In this type of system, a sample of the exhaust gas emitted out of the combustor is sampled and analyzed to determine its composition. It has been found that this type of system has a high degree of reliability, but it is considered to be slow and expensive, as well as require add-on hardware. Another consideration involved with exhaust gas measurement systems is the need for close monitoring of the system, which is undesirable in many applications that preferably are operated automatically at remote locations.
Accordingly, it would be desirable for a flame detection system to be developed for gas turbine engine combustors which is reliable, relatively inexpensive, requires no additional hardware, operates in near "real time," has a high degree of sensitivity, and can be controlled automatically from a remote location.